Many medicament delivery devices such as injectors are often developed for self-administration, i.e. the user performs the injection. In order to have a simple handling of the device it is often desirable to have it as pre-assembled as possible. Therefore often the injector is delivered to the user with an injection needle pre-attached.
Another aspect of attachment of injection needles to medicament containers is that the rear end of the injection needle often protrudes into the interior of the container. This could be a drawback if the medicament reacts with the material of the needle when exposed for a period of time. In that respect it would be desirable to have the rear part of the needle outside the container until the injection is to be performed. On the other hand, this then requires that the rear end of the needle could be moved fairly easily into the container and also that the rear end of the needle is kept in a sterile environment until it is moved into the container.
A few attempts have been done to solve this problem. Document U.S. Pat. No. 7,374,558 discloses an auto-injector having drive means for automatic penetration and injection. At the front end of the injector a sealed compartment is arranged, in which a sterile injection needle is arranged. When the injector is activated, the medicament container is pushed forward, whereby a membrane at the front end of the container is penetrated by the rear end of the needle. After this the container and the needle is advanced further, causing a penetration of the patient's skin. After penetration the injection is performed automatically.
Documents U.S. Pat. Nos. 6,743,203 and 5,658,259 disclose similar auto-injectors having a needle positioned in a sterile compartment at the front end of the injector, and where the rear of the needle penetrates the medicament container upon activation in that the container is pushed forward. Subsequent steps are penetration and injection.
The above mentioned injectors require a lot of components and it is relatively complicated to sterilize the injection needle and keep it sterile. Further, for multi-dose injectors requiring a needle change before each injection, the above mentioned solutions cannot be used.
Documents U.S. Pat. Nos. 2,828,742 and 3,916,893 disclose injectors having needles that are attached into a proximal neck portion of a medicament container such that a distal end of the injection needle penetrates a membrane of the medicament container when a needle holder is distally displaced. One of the reasons for the design according to '742 and '893 is to keep a zone sterile between the medicament container and the needle. In '742, the needle holder is distally displaced by merely gripping a surrounding needle sheath that is of a flexible material, such as rubber, thereby providing a risk of accidental needle sticks. Further, there is no locking/preventing means between the sheath and the cap/ferrule, which is a disadvantage if a user/patient removes the sheath before the distal end of the injection needle penetrates the membrane, since the proximal end of the needle may be contaminated or/and it may be difficult to position the sheath again in connection with the cap/ferrule. In '893, the needle holder is distally displaced by threading the sheath in one direction onto a cap/syringe body. There are no locking/preventing means between the needle holder and the cap/syringe body after the needle holder has been distally displaced. This is a disadvantage if the press fitting between the needle holder and the cap/syringe body is not enough to withstand the pressure exerted when expelling a liquid. Moreover, the removal of the sheath is not either intuitive since the user/patient has to rotate the sheath back to remove it.